Ultrafast Internal Conversion Dynamics through the on-the-Fly Simulation of Transient Absorption Pump-Probe Spectra with Different Electronic Structure Methods

Chao Xu; Kunni Lin; Deping Hu; Feng Long Gu; Maxim F Gelin; Zhenggang Lan

doi:10.1021/acs.jpclett.1c03373

Ultrafast Internal Conversion Dynamics through the on-the-Fly Simulation of Transient Absorption Pump-Probe Spectra with Different Electronic Structure Methods

J Phys Chem Lett. 2022 Jan 20;13(2):661-668. doi: 10.1021/acs.jpclett.1c03373. Epub 2022 Jan 13.

Authors

Chao Xu¹, Kunni Lin¹, Deping Hu², Feng Long Gu¹, Maxim F Gelin³, Zhenggang Lan²

Affiliations

¹ Key Laboratory of Theoretical Chemistry of Environment, Ministry of Education; School of Chemistry, South China Normal University, Guangzhou, 510006, P. R. China.
² Guangdong Provincial Key Laboratory of Chemical Pollution and Environmental Safety and MOE Key Laboratory of Environmental Theoretical Chemistry, SCNU Environmental Research Institute, School of Environment, South China Normal University, Guangzhou, 510006, P. R. China.
³ School of Sciences, Hangzhou Dianzi University, Hangzhou, 310018, P. R. China.

PMID: 35023755
DOI: 10.1021/acs.jpclett.1c03373

Abstract

An on-the-fly surface-hopping simulation protocol is developed for the evaluation of transient absorption (TA) pump-probe (PP) signals of molecular systems exhibiting internal conversion to the electronic ground state. We study the nonadiabatic dynamics of azomethane and the associating TA PP spectra at three levels of the electronic-structure theory, OM2/MRCI, SA-CASSCF, and XMS-CASPT2. The impact of these methods on the population dynamics and time-resolved TA PP signals is substantially different. This difference is attributed to the strong non-Condon effects that must be taken into account for the proper understanding and interpretation of time-resolved TA PP signals of nonadiabatic polyatomic systems. This shows that the combination of the dynamical and spectral simulations definitely provides more accurate and detailed information on the microscopic mechanisms of photophysical and photochemical processes. Hence the simulation of time-resolved spectroscopic signals provides another important dimension to examine the accuracy of quantum chemistry methods.